1. Field of the Invention
The present invention relates to a technical field of a photo touch panel, more particularly, relates to a photoelectric sensor and a photoelectric touch panel.
2. Description of the Related Art
When exposed to a visible light, the α-Si TFT (Thin Film Transistor) generates a relative large photo current. In a TFT-LCD (Thin Film Transistor Liquid Crystal Display), in order to achieve a small drain current, it is necessary to block the channel of the α-Si TFT from light as can as possible. For example, a metal material is used at one side of the α-Si TFT adjacent to a backlight to block the light from the backlight, a black matrix is used at the other side of the α-Si TFT adjacent to a color film substrate to block the light from outside environment. In fact, the drain current of the α-Si TFT is increased with the increase of the intensity of the light irradiating on the α-Si TFT. Herein, the drain current of the α-Si TFT is referred as the photo current.
With the characteristic of the photo current of the α-Si TFT, a photoelectric conversion and a light input can be accomplished. As a result, a photo touch panel can be incorporated into the TFT-LCD, for achieving both the display function and the touch function on the TFT-LCD.
FIG. 1 shows a conventional photoelectric sensor of a photo touch panel in prior arts. As shown in FIG. 1, the photoelectric sensor comprises a photoelectric TFT T1, a readout TFT T3 and a capacitor C1. The photoelectric TFT T1 is constructed to convert a photo signal into an electrical signal. The readout TFT T3 is constructed to read out the electrical signal and output the read electrical signal to an external circuit to further process the electrical signal. The gate electrode and the source electrode of the photoelectric TFT T1 are connected to each other, and the photoelectric TFT T1 is always in an integration state when reading each frame of data. Particularly, when there is an interference of environment light during operation of the photoelectric TFT T1, it causes a large interference noise. When the intensity of the light is strong, for example, under the direct irradiation of the sunlight, the photo current generated in the photoelectric TFT T1 is very large. Furthermore, the integration time of the TFT T1 is relative long, thereby the TFT T1 may occur the charging saturation and cannot normally respond to a photo signal input from a light pen for inputting the photo signal into the photoelectric sensor.